Competitive interactions in social foragers

Empirical and theoretical investigations of aspects of the ideal free distribution (IFD) are presented, with particular emphasis on interactions between individuals within foraging groups. An overview of the theory is presented, and the implications of the work included in this thesis to ideal free distribution theory are discussed. The effect of group size on the relative competitive ability of individual fish within a foraging group is shown to be dependent upon the difference in body size between two focus individuals in a group, but this difference itself has no direct effect on relative competitive ability. A subsequent empirical test of a novel mathematical tool reveals that there is no simple general rule for describing how relative competitive ability will change with group size, and that very specific knowledge of the system under study is needed in order to produce robust predictions. The relative abilities of individual chiclids to obtain food under scramble competition are shown to be highly repeatable between trials. However, when given a choice between two patches differing only in their temporal variability in input about an identical mean, an individual's rank based on intake in one patch was uncorrelated with either its uptake in the other patch or its intake in either of two different trial types. The basis for, and consequence of, this dependence of relative competitive ability on the context of the foraging situation are discussed. The general case (previously unexposed in the literature) where the effect of interference can vary between patches is examined. Simulations from an individual-based model reveal a decrease in the number of stable equilibrium distributions as the competitive advantage of the dominant phenotype declines in one patch, leading eventually to a single stable equilibrium, in which both phenotypes are found on both patches